Nilai x yang memenuhi persamaan sin 3x + sin x = 2 cos x untuk 0 ≤ x ≤ π/2 adalah... A.π/6 dan π/4 B.π/6 dan π/3 C.π/6 dan π/2 D.π/4 dan π/3 E.π/4 dan π/2

sin 3x + sin x = 2 cos x
2 sin (3x + x)/2 cos (3x - x)/2 = 2 cos x
2 sin 2x cos x = 2 cos x
Sin 2x cos x = cos x
Sin 2x cos x - cos x = 0
Cos x (sin 2x - 1) = 0
1) cos x = 0
=> cos x = cos 90°
=> x = 90° = π/2

2) (sin 2x - 1) = 0
=> sin 2x = 1
=> sin 2x = sin 90°
=> 2x = 90°
=> x = 45° = π/4